(1) Field of the Invention
The present invention relates to a process for improving the properties of wood-base carbon activated in the presence of phosphoric acid. More particularly, this invention relates to controlling the amount of certain metal salts dissolved in the process acid.
(2) Description of the Prior Art
In the production of activated carbon from wood, sawdust is mixed with various chemical agents, carbonized and often subsequently activated by gas reactions. Wood-base carbons have been used for decolorizing by contacting solutions with the activated carbon. One such example appears in U.S. Pat. No. 1,383,755 wherein alkali metal sulfates were added to sawdust and other materials to assist in activation. Another use for carbons is in the gas phase for adsorption of hydrocarbon vapor. An example of this type of carbon is described in U.S. Pat. No. 3,764,561.
These and other patents have sought to improve one adsorbing property or another using varied techniques including the application of metal salts. The use of such metals is generally characterized by large proportions of salt relative to the wood, high temperatures (around 1,800.degree. F.), and frequently contact with oxidizing gases at 1,500.degree.-1,800.degree. F.
Activated carbon can also be made from wood by carbonizing it in the presence of phosphoric acid at temperatures around 800.degree.-1,300.degree. F. It has now been found that by controlling the amount of certain dissolved metals in this process acid during heat treatment, activated carbons having desirable decolorizing ability and desirable gas adsorbing ability, or both, may be obtained.
It is, therefore, the general object of this invention to provide a process for improving the decolorizing ability and the gas adsorbing ability of wood-base activated carbon produced in the presence of phosphoric acid.
Another object of this invention is to provide an improved process for producing wood-base activiated carbon by controlling the amount of dissolved metal salt in the process acid during activation.
Other objects, features, and advantages will be evident from the following detailed description of the invention.